Telephone communication between two personal computers (PCs) over a local area network (LAN) is known. Voice over IP (VoIP) communication, which provides Internet telephone communication between two PCs over the Internet, is also known.
A technique in which, in response to a connection request from the Internet, a server in a DMZ (DeMilitarized Zone) sends a connection request to a terminal on an intranet via a firewall is known in, for example, literature “H323ProxyServer” of INTEC Web and Genome Informatics Corporation [searched on Oct. 23, 2002, URL:http:www3.noc.intec.co.jp/products/H323Proxy/]. However, once an access from such a server to a terminal on an intranet is allowed, there arises the possibility that a malicious user may perform an illegal access or the like to an apparatus on the intranet.
There is a need for realizing the VoIP communication between a terminal connected to an intranet having an firewall and another terminal connected to the Internet. However, it is not known how the VoIP communication can be realized between such two terminals, while allowing an firewall that is necessary for security to effectively operate.
The inventors have recognized that the VoIP communication between a terminal on an intranet and another terminal on the Internet can be realized by terminating calls for both of the terminals in a DeMilitarized Zone (DMZ) between the intranet and the Internet and associating the one call with other call.
It is an object of the invention to realize a call to be established between a terminal connected to an intranet and another terminal connected to an external network.
It is another object of the invention to realize multimedia communication between a terminal connected to an intranet and another terminal connected to an external network.
It is a further object of the invention to realize, in a safer manner, a call to be established between a terminal connected to an intranet and another terminal connected to an external network.